docs: add short mode query sample & test

[shollyman]

internal issue: b/353790025

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/client_query_shortmode.py:17, tag bigquery_query_shortquery

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[Linchin]

LGTM.